Abstract
Label-free imaging of living cells below the optical diffraction limit poses great challenges for optical microscopy. Biologically relevant structural information remains below the Rayleigh limit and beyond the reach of conventional microscopes. Super-resolution techniques are typically based on the non-linear and stochastic response of fluorescent labels which can be toxic and interfere with cell function. In this paper we present, for the first time, imaging of live cells using sub-optical wavelength phonons. The axial imaging resolution of our system is determined by the acoustic wavelength (λa = λprobe/2n) and not on the NA of the optics allowing sub-optical wavelength acoustic sectioning of samples using the time of flight. The transverse resolution is currently limited to the optical spot size. The contrast mechanism is significantly determined by the mechanical properties of the cells and requires no additional contrast agent, stain or label to image the cell structure. The ability to breach the optical diffraction limit to image living cells acoustically promises to bring a new suite of imaging technologies to bear in answering exigent questions in cell biology and biomedicine.
Highlights
Optical microscopy is possibly the most powerful technique used in the life sciences to study cell biology and remains an extremely active global research area, continuing to drive advances in biomedicine
This is the same fundamental mechanism to obtain a measurement presented here, spontaneous Brillouin scattering is an inefficient process since it relies on thermally generated phonons within the sample and requires high optical fluxes to obtain sufficient signal-to-noise ratio (SNR) that are incompatible with living cells, the method is intrinsically optically-limited in resolution because the thermal phonons are incoherent
The design parameters of this novel transducer are tuned to produce mechanical as well as optical resonances in the desired performance bands. This configuration offers several key advantages over other phonon detection methods: significantly reduced exposure of the sample to both pump and probe beams, increase in signal amplitude through mechanical resonance within the transducer and enhanced thermal management by the use of a high-thermal-conductivity substrate. These advantages manifest as greatly improved signal-to-noise ratio (SNR) and minimised thermal disruption to the sample
Summary
Optical microscopy is possibly the most powerful technique used in the life sciences to study cell biology and remains an extremely active global research area, continuing to drive advances in biomedicine. The study of dynamic internal processes involving sub-optical structures (
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